1. Field of the Invention
The present invention relates to the field of semiconductor wafer processing equipment. More particularly, the present invention relates to a method and apparatus for aligning a wafer on a wafer support member.
2. Background of the Related Art
In the fabrication of integrated circuits, the various processes, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and etch processes, are often carried out in a vacuum environment to, among other things, reduce the particulate level to which the wafers are exposed. Wafers are introduced into a vacuum processing system through a loadlock where robots within the vacuum processing system move the wafers from the loadlock into a transfer chamber and then sequentially through the system positioning the wafers in a series of processing chambers.
The processing steps carried out within the vacuum chambers typically require the deposition, or etching of multiple metal, dielectric and semiconductor film layers on the surface of a wafer. During these processing steps, one must properly align and secure the wafer in the processing chamber in which the desired deposition or etch process is performed.
Typically, the wafer is supported in the chamber on a support member, commonly called a susceptor or pedestal. The wafer is placed on or secured to, the upper surface of the support member prior to the deposition or etch process. To ensure proper processing of the wafer, the wafer must be properly aligned relative to the support member. The position of the support member in the chamber is selected to provide a desired spacing and relative geometry between the generally planar surface of the wafer and other portions of the process chamber such as a gas plate in a CVD process or a target in a PVD process.
Generally, a shadow or clamp ring is used to shield the edge of a wafer and/or, in the case of a clamp ring, secure the wafer to the support member. Although the present invention is equally applicable to both shadow rings and clamp rings, the following description will refer primarily to shadow rings such as those typically used in CVD processes. In addition to acting as a shield, shadow rings also function in wafer capturing or alignment on the support member. Wing members extend downwardly and outwardly from the shadow ring to form a funnel. As the support member moves the wafer upward into the processing position, the support member moves the wafer into the funnel which directs the wafer into alignment with the shadow ring and the support member. Consequently, the funnel applies vertical and lateral forces to the wafer when the slanted wing members achieve lateral alignment of a misaligned wafer with the shadow ring and support member as the support member moves the wafer to the top end of the funnel and the shadow ring settles on the support member.
A primary goal of wafer processing is to obtain as many useful die as possible from each wafer. Many factors influence the processing of wafers in the chamber and effect the ultimate yield of die from each wafer processed therein including the existence of contaminants within the chamber that can attach to the wafer and contaminate one or more die therein. The processing chambers have many sources of particle contaminants which, if received on the wafer, reduce the die yield. One source of particulate contamination occurs when a misaligned wafer is introduced into the chamber. As the wing members of the shadow ring align with the wafer, the wafer slides on the flat surface of the support member and, due to the frictional forces between the wafer and the support member, may create particulate contaminants. In some cases, the frictional forces between the wafer and the support member cause the misaligned wafer to actually move the shadow ring, thereby preventing proper alignment of the wafer and reducing repeatability of the zone of exclusion shielded by the shadow ring and the process.
Prior efforts aimed at reducing the creation of particles have reduced the alignment movement of the wafer on the support member and simply increased the amount of overhang by the shadow ring. In this way, the shadow ring is able to cover the wafer without substantial movement of the wafer. One way that this is accomplished is by increasing the diameter of the shadow ring funnel upper end so that this diameter is larger relative to the diameter of the wafer and the support member. Thus, rather than substantially moving the wafers to align them, these systems simply accept a greater misalignment and accept greater coverage of the wafer upper surface area.
However, a second factor influencing the processing of wafers in the chamber and affecting the ultimate yield of die from each wafer processed therein is the repeatability of the positioning of the wafer and the area covered by the shadow ring. The wafer must be properly aligned relative to the support member and the shadow ring to ensure that the film is properly deposited on the wafer. Therefore, these prior efforts that avoid alignment of the wafer and cover more surface area are not acceptable.
It would, therefore, be desirable to provide a relatively simple system and method for reducing the coefficient of friction between the support member and the wafer that would allow alignment of the wafer without substantial particle generation.